The present disclosure relates to a fixing device fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
An electrographic image forming apparatus, such as a copying machine or a printer, includes a fixing device fixing a toner image on a recording medium, such as a sheet. In the fixing device, various manners are applied. As a general manner, a so-called “heat roller manner” is cited, in which the heat roller stores a heating source inside and a fixing nip is formed by making the heat roller come into pressure contact with a pressuring member. The fixing device in the heat roller manner heats and pressures the toner image and recording medium by the fixing nip formed between the heat roller and pressuring member to fix the toner image on the recording medium.
On the other hand, recently, in order to make the image forming apparatus conform to a standard or a regulation regarding saving energy, shortening of a warm-up time and reduction of electric power during operation are required for the fixing device. About this point, in the above-mentioned heat roller manner, because strength to endure the forming of the fixing nip is required for the heat roller, thickness of the heat roller must be thickened, and accordingly, thermal capacity becomes large as a result.
Therefore, a so-called “belt manner” fixing device is developed, in which a fixing nip is formed by using a fixing belt having a thinner thickness and smaller thermal capacity than the heat roller. For example, there is a fixing device includes the fixing belt, a pressuring member, a nip forming member, a supporting member, a heating source, and a heat conducting member. The pressuring member comes into pressure contact with the fixing belt to form the fixing nip. The nip forming member presses the fixing belt to a side of the pressuring member. The supporting member supports the nip forming member. The heating source is arranged inside the fixing belt. The heat conducting member comes into contact with an inner circumference face of the fixing belt.
In the above-mentioned technique, in a case where the heating source faces to the supporting member, a part of radiant heat emitted from the heating source is absorbed by the supporting member and lost from the supporting member to an outside of the fixing device. Therefore, because the heating source cannot intensively heat the heat conducting member, heat conduction efficiency from the heat conducting member to the fixing belt is lowered, and accordingly, it is difficult to effectively heat the fixing belt. Moreover, in the above-mentioned technique, in a case where a part of the fixing belt is supported from the inside by the heat conducting member, a traveling track of the fixing belt is likely to become unstable.